For example, systems for producing a film or roll type plate (hereinafter, referred to as a “thin film”) having a film-type sheet with several micrometers or several ten micrometers, e.g., flooring films or various functional films, perform a cleaning process for removing impurities adhered to the surface of the roll-type thin film. In this film cleaning process, a cleaning fluid (e.g., liquid) is injected to the surface of the thin film to remove the impurities adhered to the surface of the thin film.
FIG. 1 is a schematic view showing a conventional thin film cleaning system. FIG. 2 is a graph showing a flow rate of a fluid corresponding to each hole of a nozzle tube in the system of FIG. 1.
Referring to FIGS. 1 and 2, the conventional thin film cleaning system 1 includes a fluid supplying apparatus 5 disposed in a cleaning bath 2 to be immersed in an immersion liquid 3 and capable of injecting a cleaning fluid so that impurities present in the surface (the upper and/or lower surface) of a thin film 4 which is successively moved while being immersed in the immersion liquid 3 stored in the cleaning bath 2.
The conventional fluid supplying apparatus 5 includes a supply tube 6 installed in the cleaning bath 2 to receive a cleaning fluid from the outside, and a nozzle tube 7 diverged vertically from the supply tube 6 to uniformly inject the cleaning fluid toward the thin film 4 with a predetermined pressure. The nozzle tube 7 is hollow with closed ends on both sides and has a plurality of holes 8 in a length direction. The thin film 4 is rolled on a plurality of rollers 9 and moves at a predetermined speed. The cleaning fluid injected from the holes 8 gives a predetermined pressure to the surface of the thin film 4 moving in association with the immersion liquid 3. This pressure is at the level allowing impurities present on the surface of the thin film 4 to be removed. In other words, the holes 8 formed in the nozzle tube 7 have a kind of nozzle function. Though FIG. 1 shows that the fluid supplying apparatus 5 is disposed above the thin film, the nozzle tube 7 may also be located only below the thin film 4 or both above and below the thin film 4.
However, in the conventional thin film cleaning system 1, since the diameter of the holes 8 for injecting a cleaning fluid is smaller than the diameter of the nozzle tube 7, the cleaning fluid supplied into the nozzle tube 7 from the supply tube 6 flows faster while passing through the holes 8. The increased flow rate of the cleaning fluid collides with the wall of the cleaning bath 2 and returns, and in this process, the flowing pattern of the fluid in the cleaning bath 2 gets complicated. Such a complicated flow pattern applies irregular pressure to the thin film 4 moving above or below the nozzle tube 7. If the pressure deviation increases, for example, the thin film 4 may fold or droop. This phenomenon, namely the fact that the thin film 4 progresses to the next process over the roller 9 in a state of being folded, may give a serious influence when the thin film 4 fractures.